The present invention relates generally to semiconductor device packages, and more particularly to packages with a gel filled cavity.
For certain semiconductor device packages, such as those that include pressure-sensing dies, it is known to apply a pressure-sensitive gel material over the pressure-sensing die to protect the die while still allowing the die to sense the atmospheric pressure outside of the package.
In some package designs having one or more dies, the gel fills the entire bottom portion of the package housing and is intended to cover all of the dies as well as any bond wires used to connect the dies to one another and/or to package leads. Unfortunately, due to the mechanical properties of some gels and some housing materials, when the gel is dispensed into the cavity, the gel's meniscus behavior results in the top surface of the gel having a concave shape. The concavity of the gel can increase during staging and curing, where staging refers to the time period from the dispensing of the gel until the beginning of the curing process.
FIGS. 1(A) and 1(B) show simplified cross-sectional side views of a conventional partially assembled semiconductor device package 100 having two dies 102 and 104 mounted within a package housing 106 that is partially filled with gel 108 and having at least one interconnecting bond wire 110. Other bond wires, if any, are not shown. FIG. 1(A) shows the package 100 just after the gel 108 has been dispensed, while FIG. 1(B) shows the package 100 after the gel 108 has been cured.
As shown in FIG. 1(A), the uncured gel 108 has a slightly concave top surface, while the top surface of the cured gel 108 in FIG. 1(B) has greater concavity. This greater concavity can result from the uncured gel 108 creeping up the walls of the housing 106 due to capillary action and/or shrinkage of the gel 108 during the curing process.
Unfortunately, as represented in FIG. 1(B), the increase in the concavity of the gel 108 can result in the exposure of portions of one or more of the bond wires 110 outside of the cured gel.
Furthermore, the concavity of the cured gel 108 in FIG. 1(B) corresponds to a relatively large variation in the thickness of the gel 108 across the width of the package 100, with the gel 108 being thicker at the edges of the package and thinner at the middle of the package.
Conventional package qualification processes involve thermal cycling during which the fully assembled packages are repeatedly heated up and cooled down over the range of expected operating temperatures for the package. The varying gel thickness across the width of the package can result in relatively large internal stresses during thermal cycling that can cause permanent damage to the package, such as broken and/or disconnected bond wires. Accordingly, it would be advantageous to have an assembly process that ensures the bond wires are covered with gel.